RU2418374C2 - Method to do pre-cording based on phase shift and device for its support in wireless communication system - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: method includes detection of a diagonal matrix to provide different phase angles to each of multiple antennas as a part of matrix of pre-coding based on phase shift, selection of a unitary matrix from the first coding table as a part of matrix of pre-coding based on phase shift; and pre-coding relative to symbols associated with subcarriers, on the basis of a diagonal matrix and a unitary matrix.

EFFECT: improved functioning of communication.

14 cl, 8 dwg, 6 tbl

Description

FIELD OF THE INVENTION

The present invention relates to a method for performing phase-shift-based precoding, and more particularly, to a method for performing phase-shift-based precoding and a device for supporting it in a wireless communication system.

BACKGROUND

With the increasing use and popularity of various multimedia services and the widespread use of communication services, the demand for wireless services is rapidly growing. In order to meet changing needs, it is important to increase the throughput of the communication system. One way to increase throughput involves finding a new available frequency band and improving the efficiency of existing resources.

As an example of improving the utilization of existing resources, the transmitter and receiver may be equipped with multiple antennas for efficient use of resources in the spatial domain to achieve diversity gain. Moreover, multiple antennas provide parallel transmission of data through each antenna to provide increased transmission throughput.

A method related to transmitting and receiving data using multiple antennas may be represented by a multi-input multi-output (MIMO) system using orthogonal frequency division multiplexing (OFDM).

SUMMARY OF THE INVENTION

TECHNICAL SOLUTION

Accordingly, the present invention is directed to a method for performing phase shift-based precoding and a device for supporting it in a wireless communication system, which essentially eliminate one or more problems due to limitations and disadvantages of the prior art.

An object of the present invention is to provide a method for transmitting data using phase shift-based precoding in a multi-antenna system using multiple subcarriers.

Another objective of the present invention is to provide a device for transmitting data using phase-shift-based precoding in a multi-antenna system using multiple subcarriers.

Additional advantages, objects, and features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art after studying the following, or may be learned from practicing the invention. The objectives and other advantages of the invention can be realized and achieved through the design shown in detail in its written description and claims, as well as in the accompanying drawings.

To achieve these goals and other advantages, and in accordance with the purpose of the invention, which is embodied and broadly described in the materials of this application, a method for transmitting data using phase shift-based precoding in a multi-antenna system using multiple subcarriers includes determining the diagonal matrices to provide different phase angles of each of the multiple antennas as part of a matrix based on phase shift precoding, the choice is unitary nth matrix from the first coding table as part of a phase shift-based matrix of precoding and performing precoding with respect to the symbols associated with the subcarriers based on the diagonal matrix and the unitary matrix.

In yet another aspect of the present invention, a device for transmitting data using phase shift-based precoding in a multi-subcarrier multi-antenna system includes a precoding matrix determining module configured to determine a diagonal matrix for at least one phase shift and a coding table and a matrix based on a phase shift precoding based on a diagonal matrix and a unitary matrix, and modes l precoding configured to perform precoding on symbols of corresponding subcarriers based on the diagonal matrix and the unitary matrix.

It should be understood that both the foregoing general description and the following detailed description of the present invention are illustrative and explanatory and are intended to provide further clarification of the claimed invention.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate embodiment (s) of the invention and, together with the description, serve to explain the principle of the invention. In the drawings:

1 is an exemplary diagram illustrating a structure of a transmitter and a receiver for a MIMO system;

2 is an exemplary diagram illustrating a transmitter of a multi-antenna system using a CDD scheme;

3 is an exemplary diagram illustrating the use of a phase sequence;

4 is an exemplary diagram illustrating a transmitter and receiver of a multi-antenna system using a table-based coding scheme of precoding;

5 is an exemplary diagram illustrating a transmitter and a receiver for performing phase shift-based precoding;

6 is an exemplary diagram illustrating two types of phase-shift-based precoding based on delay sample size;

7 is an exemplary diagram illustrating an OFDM-based SCW transmitter and receiver using phase shift-based precoding; and

8 is an exemplary diagram illustrating an OFDM-based MCW transmitter and receiver using phase shift-based precoding.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, detailed reference will be made to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to identical or similar parts.

1 is an exemplary diagram illustrating a structure of a transmitter and a receiver for a MIMO system. 1, the transmitter comprises a channel encoder 101, a display unit 103, a series-parallel (S / P) converter 105, and a multi-antenna encoder 107. More specifically, the channel encoder 101 may attach repeated (or additional) bits to transmission data bits, for in order to reduce the mutual interference caused by the channel and / or noise. The mapper 103 may convert the data bits to data symbols, and the S / P converter 105 may align the data symbols for distribution on subcarriers. In conclusion, multi-antenna encoder 107 can convert data symbols arranged in parallel to spatio-temporal signals.

In addition, the receiver comprises a multi-antenna decoder 109, a parallel-to-serial (P / S) converter 111, a reverse mapping unit 113, and a channel decoder 115. The functions of the multi-antenna decoder 109, P / S converter 111, inverse display unit 113, and receiver channel decoder 115 are opposite to those of the multi-antenna encoder 107, S / P converter 105, display unit 103 and transmitter channel encoder, respectively, and therefore a detailed description will be omitted.

In a multi-antenna OFDM system, various schemes can be used to increase the reliability of data transmission. These schemes include a space-time code (STC) scheme and a cyclic delay diversity (CDD) scheme. STC and CDD schemes can be used to achieve spatial diversity. Moreover, the circuitry further includes a beamforming scheme and a precoding scheme that can be used to increase the signal to noise ratio (SNR).

The STC scheme and the CDD scheme are typically used in an open loop system without feedback information to increase the reliability of the transmission data. Moreover, a beamforming scheme and a precoding scheme are typically used in a closed-loop system using feedback information to optimize SNR.

In particular, as a scheme for increasing the gain from spatial diversity and SNR, a CDD scheme and a precoding scheme, respectively, can be discussed in more detail, as presented below.

First, the CDD scheme provides each antenna of a multi-antenna system with the ability to transmit OFDM signals having a different delay or having different sizes, so that the receiver can achieve a gain from frequency diversity.

2 is an exemplary diagram illustrating a transmitter of a multi-antenna system using a CDD scheme.

After the OFDM symbols are processed by the S / P converter and multi-antenna encoder and then transmitted through each antenna, a cyclic prefix (CP) can be added (or attached) to the OFDM symbols during transmission to the receiver. A CP may be added to OFDM symbols to prevent inter-channel interference. Here, the data sequence sent to the first antenna for transmission does not have a CP, but the data sequence sent to subsequent antennas for transmission contains a CP attached to it. That is, data sequences sent to subsequent antennas have a predetermined number of cyclic delay bits applied to them.

If such a cyclic delay diversity scheme is applied in the frequency domain, the cyclic delay can be expressed by multiplying a phase sequence. Figure 3 is an exemplary diagram illustrating the application of a phase sequence. 3, phase sequences (e.g., a sequence of 1 phases ~ a sequence of M phases), each of which is configured differently for each antenna in the frequency domain, are multiplied, and then applied to the inverse fast Fourier transform (IFFT). Further, the converted data may be transmitted to the receiver, and this flowchart of FIG. 3 may be referred to as a phase shift diversity scheme.

If a phase shift diversity scheme is used, a channel with uniform fading can be converted to a frequency selection channel. In addition, frequency diversity gain can be achieved by channel coding, and / or multi-user diversity gain can be achieved by frequency selection scheduling.

Secondly, the precoding scheme includes a table-based coding scheme of precoding and a quantization scheme. More specifically, a precoding table based coding scheme may be used if a constant amount of closed loop system feedback information is returned by feedback. In addition, a quantization scheme may be used to feedback the quantized channel information. The table-based coding scheme of the precoding sends, as feedback information, the index of the precoding matrix, which is known to both the transmitter and the receiver, to the transmitter in order to achieve SNR gain.

4 is an exemplary diagram illustrating a transmitter and receiver of a multi-antenna system using a table-based coding scheme of precoding. According to figure 4, each of the transmitter and receiver has a limited number of precoding matrices (for example, P ₁ - P _L ). In the process, the receiver uses the channel information to send as feedback information to the transmitter the optimal index of the precoding matrix (for example, “ index l ”). In response, the transmitter applies index 1 to the corresponding data ( X _l −X _Mt ) of the transmission of the precoding matrix.

Table 1 is an example of a coding table that can be used when 3-bit feedback information is used in a system (eg, IEEE 802.16e system) that supports two transmit antennas and a spatial multiplex coefficient of 2.

[Table 1] Matrix index
(binary) Column 1 Column 2 Matrix index
(binary) Column 1 Column 2 000 one 0 000 0.7941 0.6038-j0.0689 0 one 0.6038 + j0.0689 -0.7941 001 0.7940 -0.581-j0.1818 101 0.3289 0.6614-j0.6740 -0.5801 + j0.1818 -0.7940 0.6614 + j0.6740 -0.3289 010 0.7940 0.0576-j0.6051 110 0.5112 0.4754 + j0.7160 0.0576 + j0.6051 -0.7940 0.4754-j0.7160 -0.5112 011 0.7941 -0.2978 + j0.5298 111 0.3289 -0.8779 + j0.3481 -0.2978- j0.5298 -0.7941 -0.8779-j0.3481 -0.3289

As discussed, a phase shift diversity scheme can be used to achieve closed loop diversity diversity gain and can also achieve frequency planning diversity gain. However, the spatial compaction coefficient is 1 for a phase shift diversity scheme, and therefore, it cannot be assumed to transmit data at a high transmission rate. In addition, it can be difficult to expect frequency diversity diversity gain and frequency planning diversity gain in a phase shift diversity scheme if resources are assigned in a fixed manner.

In addition, the precoding scheme based on the coding table, as discussed, can use a small amount of feedback information (or index information) and has a high spatial multiplexing coefficient, and accordingly, can efficiently transmit data. However, since this circuit requires a stable channel condition due to its dependence on feedback information, this circuit may be difficult if the channel state is unstable. Moreover, this precoding scheme based on the coding table is limited to use only in closed loop systems.

In order to respond to these potential problems associated with a phase shift diversity scheme and / or a coding table based precoding scheme, the following discussions will be given.

5 is an exemplary diagram illustrating a transmitter and a receiver for performing phase shift-based precoding. More specifically, phase shift-based precoding refers to multiplying a different sequence of phases by data streams that must be transmitted through each of the multiple antennas. Typically, small cyclic delay values are used to form a phase sequence. In this case, from the point of view of the receiver, diversity with frequency selection can be achieved, and the channel size increases or decreases depending on the frequency domain.

5, a transmitter may implement scheduling diversity by assigning receivers (eg, mobile devices) to parts of the frequency domain where the channel condition is good (or acceptable). Here, some parts of the frequency domain have a large frequency band and are less prone to fluctuations caused by relatively small cyclic delay values. In order to apply cyclic delay values that increase or decrease uniformly to each antenna, a phase shift-based precoding matrix, P , can be used as expressed in equation 1.

[Equation 1]

(i=1,…, N _t , j=1, 1,…, R) обозначает комплексный весовой коэффициент, определенный согласно k. Более того, N _t обозначает количество передающих антенн или виртуальных антенн, и R обозначает коэффициент пространственного уплотнения. Здесь значение комплексного весового коэффициента может быть переменным, согласно индексу символов OFDM и соответствующим поднесущим, умноженным на антенны. В дополнение, значение комплексного весового коэффициента может определяться состоянием канала и/или информацией обратной связи. Предпочтительно матрица предварительного кодирования, P, по уравнению (1) конфигурируется с использованием унитарной матрицы, чтобы снижать потери в емкости канала многоантенной системы.In equation (1), k denotes a subcarrier index or an index of an individual frequency bandwidth, and

(i = 1, ..., N _t , j = 1, 1, ..., R ) denotes the complex weight coefficient determined according to k . Moreover, N _t denotes the number of transmitting antennas or virtual antennas, and R denotes the spatial compaction coefficient. Here, the value of the complex weighting coefficient may be variable according to the OFDM symbol index and corresponding subcarriers multiplied by antennas. In addition, the value of the complex weight can be determined by the state of the channel and / or feedback information. Preferably, the precoding matrix, P , according to equation (1) is configured using a unitary matrix in order to reduce the channel loss of the multi-antenna system.

The following equation can be used to express the channel capacity of a closed loop multi-antenna system to determine the elements (or components) of a unitary matrix.

[Equation 2]

In equation (2), H denotes a multi-antenna channel matrix having a size of N _r × N _t , and N _r denotes the number of receiving antennas. If equation (2) is applied to a phase shift-based precoding matrix P , the result can be expressed as shown in equation (3).

[Equation 3]

According to equation (3), in order to minimize or eliminate the channel capacity loss, PP ^H must be a unit matrix. Essentially, the phase-shift-based matrix P must satisfy the following condition in equation (4).

[Equation 4]

PP ^H = I _N

In order for the matrix P of the phase shift-based precoding to be converted to a unit matrix, two conditions must be satisfied. That is, at the same time, it is necessary to satisfy the power limitation condition and the orthogonality restriction condition. The power constraint condition refers to setting the size of each column of the matrix to 1. In addition, the orthogonality constraint condition refers to making each column orthogonal (or the columns are orthogonal to each other). Equation (5) and equation (6) are examples of such.

[Equation 5]

[Equation 6]

The discussions above for equations (2) - (6) relate to the unitary matrix. Further discussions of the unitary matrix relate to a phase shift-based precoding matrix having a 2 × 2 matrix size.

Equation (7) represents a general phase shift-based precoding matrix having a spatial multiplier of 2 for two transmit antennas.

[Equation 7]

In equation (7), α _i , β _i ( i = 1, 2) are real numbers, θ _i (i = 1, 2, 3, 4) is the phase value, and k is the index of the subcarrier of OFDM signals.

In order to convert the precoding matrix (for example, equation (7)) into a unit matrix, it is necessary to satisfy the condition of power restriction by equation (8) and the condition of orthogonality restriction by equation (9).

[Equation 8]

[Equation 9]

In equations (8) and (9) * denotes a complex conjugate. If a phase-shift-based precoding matrix having a size of 2 × 2 satisfies equations (7) - (9), such a matrix can be expressed as shown in equation (10).

[Equation 10]

According to equation (10), θ ₂ and θ ₃ maintain an orthogonal relationship based on the satisfaction of the orthogonality restriction condition. This can be expressed as shown in equation (11).

[Equation 11]

kθ ₃  = -kθ ₂ + π

The precoding matrix may be stored in the transmitter and receiver in the form of a coding table. The coding table may include various precoding matrices using a predetermined number of different values of θ ₂ . Here, the value of θ ₂ can be configured based on channel conditions and whether feedback information is provided or not. If feedback information is provided (or used), the value of θ ₂ may be configured to be a small value. If feedback information is not provided (or not used), the value of θ ₂ can be configured to be a large value in order to achieve a gain from high frequency diversity.

In addition, the gain from frequency diversity and / or the gain from frequency scheduling can be achieved according to the sample size of the delay applied to the matrix based on the phase shift of the precoding. 6 is an exemplary diagram illustrating two types of phase shift-based precoding based on delay sample size.

6, if a large sample size of the delay (or cyclic delay) is used, the gain from frequency diversity for channel symbols can be achieved by a frequency selection cycle becoming higher due to the choice of frequency becoming shorter. It is preferable to use a large delay sample in an open loop system in which the feedback information is less reliable due to strong temporal fluctuations with respect to the channels.

In addition, if a small delay sample value is used, there may be channels from the frequency selection channels in which the channel sizes increase or decrease in the evenly fading channel (s). Moreover, if the channel sizes of a given region of the subcarriers of the OFDM signal increase, then the channel sizes of the other region of the subcarriers of the OFDM signal decrease. In other words, the opposite is true.

In this case, as for the Orthogonal Frequency Division Multiple Access (OFDMA) system, the SNR may increase if the signal is transmitted in a frequency band where channel sizes have increased for each user. In addition, a frequency band having enlarged channel sizes may be different for each user and, as a result, the system may implement scheduling diversity with respect to multiple users. Moreover, the receiver only needs to send feedback information related to the channel quality information (CQI) of the subcarriers, which may be a dedicated resource. Therefore, the size of the feedback information may also decrease.

The delay sample (or cyclic delay) for the phase shift-based precoding may be a predetermined value at the transmitter and receiver, or may be supplied via feedback information from the receiver to the transmitter. Moreover, the spatial multiplexing coefficient, R , may be a predetermined value at the transmitter and receiver, or may be supplied as feedback information by the receiver to the transmitter after the receiver calculates the spatial multiplexing coefficient during periodic measurement of channel conditions. Here, the transmitter can use the channel information returned from the receiver in feedback to calculate and / or manipulate the spatial multiplexing coefficient.

Generic Phase Shift Diversity (GPSD)

The phase shift-based precoding matrix as described above is based on a system with a number of N _t antennas ( N _t greater than or equal to 2 and is a natural number) and a spatial multiplexing coefficient R ( R> 1 is a natural number). Such a system can be expressed according to equation (12).

[Equation 12]

представляет обобщенную матрицу разнесения с фазовым сдвигом (GPSD) для k^ой поднесущей сигнала OFDM MIMO, имеющего количество N _t передающих антенн и коэффициент R пространственного мультиплексирования. Более того,

- унитарная матрица, которая удовлетворяет

и может использоваться для минимизации межсимвольных взаимных помех между символами поднесущей. В частности,

также должна удовлетворять условию унитарной матрицы, чтобы могли поддерживаться характеристики унитарной матрицы у диагональной матрицы для фазового сдвига.In equation (12)

represents the generalized phase shift diversity matrix (GPSD) for the k- ^th subcarrier of the OFDM MIMO signal having the number N _t transmit antennas and the spatial multiplexing coefficient R. Moreover,

is a unitary matrix that satisfies

and can be used to minimize intersymbol interference between subcarrier symbols. In particular,

must also satisfy the condition of the unitary matrix so that the characteristics of the unitary matrix of the diagonal matrix for the phase shift can be supported.

Equation (13) represents the relationship between the phase angle θ _i , i = 1, ..., N _{t of the} frequency domain and the time delay τ _i , i = 1, ... , N _{t of the} time domain according to equation (12).

[Equation 13]

In equation (13), N _fft denotes the number of subcarriers of the OFDM signal.

As an example of equation (12), equation (14) represents a system with two transmit antennas or virtual antennas using a 1-bit coding table.

[Equation 14]

According to equation (14), since β can be relatively easily determined as soon as α is determined, α can be pre-set by two values, and information regarding pre-set values can be returned in feedback as an index of the codebook. For example, if the index of the feedback coding table is 0, α can be 0.2, and if the index of the feedback coding table is 1, then α can be 0.8. Such values may be negotiated and shared between the transmitter and receiver.

, отдельная матрица предварительного кодирования (например, матрица Адамара-Уолша или дискретное преобразование Фурье) может использоваться для достижения разнесения с SNR.As for equation (12), as an example of a unitary matrix

, a separate precoding matrix (e.g., Hadamard-Walsh matrix or discrete Fourier transform) can be used to achieve diversity with SNR.

If the Hadamard-Walsh matrix is used, an example of the GPSD matrix with respect to equation (12) can be expressed by equation (15).

[Equation 15]

Equation (15) is based on four transmitting or virtual antennas and a spatial multiplex coefficient of 4. Here, the second matrix to the right of the equal sign (i.e. represented by units and minus ones) can be rebuilt to select a specific antenna (i.e., select an antenna) and / or adjust the spatial multiplexing coefficient (i.e., adjust the coefficient).

по уравнению (12) может поставляться на передатчик и приемник в формате таблицы кодирования. Здесь передатчик может принимать индексную информацию таблицы кодирования с приемника. После этого передатчик может выбирать унитарную матрицу соответствующего индекса из таблицы кодирования и применять уравнение (12) для конфигурирования матрицы основанного на фазовом сдвиге предварительного кодирования.Unitary matrix

according to equation (12) can be supplied to the transmitter and receiver in the format of a coding table. Here, the transmitter may receive coding table index information from the receiver. After that, the transmitter can select the unitary matrix of the corresponding index from the coding table and apply equation (12) to configure the matrix based on the phase shift of the precoding.

Equation (16) represents a rearranged unitary matrix for selecting two antennas in a system having four transmitting or virtual antennas.

[Equation 16]

In addition, the following table 2 shows a method for rebuilding a unitary matrix according to the corresponding multiplexing coefficient if the spatial multiplexing coefficient changes due to a change in time and / or channel conditions.

[Table 2]

In Table 2, the first column, the first and second columns, and / or the first to fourth columns are selected according to a multiplexing coefficient (e.g., a multiplexing factor of 1, 2, or 4). However, the multiplexing coefficient (or column selection) is not limited to the example in Table 2, but the multiplexing coefficient may be one, and any one of four columns may be selected. Moreover, if the multiplexing factor is two, any two columns from four columns can be selected (for example, 1-2, 2-3, 3-4 or 4-1).

, содержащая код Уолша 2×2 или 4×4, по уравнению (12). Здесь, таблица 2 относится к 2×2, а таблица 3 относится к 4×4.In the example above, the Hadamard-Walsh matrix is used. The following example shows the GPSD matrix to which the unitary matrix is applied.

containing the Walsh code 2 × 2 or 4 × 4, according to equation (12). Here, table 2 refers to 2 × 2, and table 3 refers to 4 × 4.

[Table 3]

[Table 4]

Time Dependent GPSD

The phase angle θ _i and / or the unitary matrix U of the GPSD matrix according to equation (12) can vary according to time. In other words, the phase angle θ _i and / or the unitary matrix U can be time-dependent. As an example, the time-dependent GPSD according to equation (12) can be expressed as shown in equation (17).

[Equation 17]

(t) представляет матрицу GPSD для k^ой поднесущей сигнала OFDM MIMO, имеющего количество N _t передающих/виртуальных антенн и коэффициент R пространственного мультиплексирования в конкретный момент времени t. Более того,

- унитарная матрица, которая удовлетворяет

и может использоваться для минимизации межсимвольных взаимных помех между символами поднесущей. В частности,

также должна удовлетворять условию унитарной матрицы, так что могут поддерживаться характеристики унитарной матрицы у диагональной матрицы для фазового сдвига.In equation (17)

( t ) represents the GPSD matrix for the k- ^th subcarrier of the OFDM MIMO signal having the number N _t transmit / virtual antennas and the spatial multiplexing coefficient R at a particular time t . Moreover,

is a unitary matrix that satisfies

and can be used to minimize intersymbol interference between subcarrier symbols. In particular,

must also satisfy the condition of the unitary matrix, so that the characteristics of the unitary matrix of the diagonal matrix for the phase shift can be supported.

Equation (18) represents the relationship between the phase angle θ _i , i = 1, ..., N _{t of the} frequency domain and the time delay τ _i , i = 1, ... , N _{t of the} time domain according to equation (12).

[Equation 18]

In equation (18), N _fft denotes the number of subcarriers of the OFDM signal.

As shown in equations (17) and (18), the time delay sample value and the unitary matrix can change over time, and the time unit can be expressed in OFDM symbol units or given time units.

As examples of a GPSD matrix, to which a matrix containing a Walsh code of 2 × 2 or 4 × 4 is applied to obtain a time-dependent GPSD, can be shown in table 5 and table 6, respectively.

[Table 5]

[Table 6]

Advanced GPSD

A third matrix may be added to the GPSD matrix comprising a diagonal matrix and a unitary matrix, as shown in equation (12), to form an expanded GPSD matrix. The enhanced GPSD matrix may be expressed as shown in equation (19).

[Equation 19]

предварительного кодирования может конфигурироваться по-разному для заданной полосы частот или заданного символа поднесущей. Более того, вновь добавленная матрица

предварительного кодирования может конфигурироваться в качестве унитарной матрицы в системе с замкнутым контуром. С добавлением или включением матрицы

предварительного кодирования может достигаться выигрыш от оптимизированного SNR.According to equation (19) and in comparison with equation (12), the extended GPSD matrix includes a precoding matrix P having a size N _t × R in front of the diagonal matrix. Therefore, the size of the diagonal matrix becomes R × R. In addition, the newly added matrix

precoding can be configured differently for a given frequency band or a given subcarrier symbol. Moreover, the newly added matrix

pre-coding can be configured as a unitary matrix in a closed loop system. With the addition or inclusion of a matrix

pre-coding can benefit from an optimized SNR.

предварительного кодирования.In addition, the transmitter and receiver may be provided with a coding table that includes a plurality of matrices

pre-coding.

In the extended GPSD matrix, at least one precoding matrix P , the phase angle θ of the diagonal matrix, and the unitary matrix U can vary in time. For this purpose, if the index of the subsequent (or next) precoding matrix P is fed back to the transmitter in terms of prescribed time units or prescribed subcarrier units, a specific precoding matrix P can be selected at the corresponding index from the coding table. In this case, the enhanced GPSD matrix may be expressed as shown in equation (20).

[Equation 20]

Referring to equation (20), a detailed description of the enhanced GPSD is described in Korean Patent No. 10-2007-0037008, filed April 16, 2007. For this reason, a discussion of enhanced GPSD will be omitted.

Phase Shift Configuration for Each Antenna

The discussions that follow describe the relationships between each phase angle θ _{Nt of the} diagonal GPSD matrix, depending on the GPSD time, the extended GPSD, and the extended GPSD time-allowed. For simplicity, the discussion is based on the phase shift ratio for each antenna relative to the time-dependent GPSD, but also applies to the other GPSD variations listed above.

Phase Shift Ratio Configuration - Embodiment 1

The phase angle of the time-dependent GPSD can be configured to increase linearity according to the index of each antenna. The relationship between each phase angle can be expressed mathematically and can be expressed as shown in equation (25).

[Equation 25] θ ₁ ( t ) = 0 ∙ θ ( t ), θ ₂ ( t ) = 1 ∙ θ ( t ) θ ₃ ( t ) = 2 ∙ θ ( t ), θ ₄ ( t ) = 3 ∙ θ ( t )

More precisely, this embodiment can achieve high performance in a uniform linear structure of the antenna array. In particular, if the spatial multiplexing factor is configured or reconfigured to be small (or low), as in the case of Table 2, a gain from optimal beamforming can be achieved. Moreover, if the unitary matrix U is defined or reconfigured to be an antenna selection type, as shown in equation 16, a high gain can be achieved.

Phase Shift Ratio Configuration - Embodiment 2

The phase angle of the time-dependent GPSD can be configured to have the same phase angle when changing the phase angle between the even-numbered antennas and the odd-numbered antennas. In a system having four antennas, the relationship between each phase angle can be expressed mathematically, as shown in equation (26).

[Equation 26] θ ₁ ( t ) = 0 ∙ θ ( t ), θ ₂ ( t ) = 1 ∙ θ ( t ) θ ₃ ( t ) = 0 ∙ θ ( t ), θ ₄ ( t ) = 1 ∙ θ ( t )

According to equation (26), the first antenna and the third antenna have the same phase angle, and the second and fourth antennas share the same phase angle. In this embodiment, the system can provide good performance in a block diagonal type of channel (for example, an antenna with mutually orthogonal polarization) if the channel power is high.

Phase Shift Ratio Configuration - Embodiment 3

The phase angle of the time-dependent GPSD can be configured so that the phase angle of an individual antenna is different from the phase angle of other antennas. For such a case, each relationship between the phase angles can be expressed as shown in equation (27).

[Equation 27] θ ₁ ( t ) = 1 ∙ θ ( t ), θ ₂ ( t ) = 0 ∙ θ ( t ) θ ₃ ( t ) = 1 ∙ θ ( t ), θ ₄ ( t ) = 1 ∙ θ ( t )

According to equation (27), if the correlation between the antenna with the second index and other antennas is high, the phase angle of the second antenna is configured in a manner different from the phase angles of other antennas. According to this embodiment, a high gain from beamforming can be achieved if the correlation between an individual antenna and other antennas is high.

The above embodiments discuss the configuration of the phase angle ratio so that each antenna matches the design of the transmit antenna. However, the phase shift ratio for each antenna can be configured differently for each antenna. Moreover, the phase shift ratio for each antenna can also be configured differently for each unit of time, and the state of the channel and / or the level of mutual interference for each antenna can be taken into account. In conclusion, the phase shift ratio for each antenna can be configured to correspond to each frequency band assigned to each antenna.

Time delay and / or unitary matrix configuration

GPSD, временная задержка τ_i(t) и унитарная матрица

зависящего от времени GPSD и временная задержка (τ_i, τ_i(t)) и унитарная матрица (

,

) расширенного GPSD могут определяться по-разному или независимо согласно различным условиям. Обсужденное ниже имеет отношение к временной задержке и/или унитарной матрице GPSD; однако, такое же обсуждение также может применяться к зависящему от времени GPSD и расширенному GPSD.Regarding the time delay τ _i and the unitary matrix

GPSD, time delay τ _i (t) and unitary matrix

time-dependent GPSD and time delay (τ _i , τ _i (t)) and unitary matrix (

,

a) Advanced GPSD can be defined differently or independently according to different conditions. Discussed below is related to time delay and / or GPSD unitary matrix; however, the same discussion may also apply to time-dependent GPSD and enhanced GPSD.

The configuration of the time delay and / or unitary matrix - option 1 implementation

Like the OFDM system, if a different frequency band is used (for example, 1.25 MHz, 5 MHz, 10 MHz, ..., 100 MHz) for each subcarrier, the time delay and / or the GPSD unitary matrix can be configured differently according to each bandwidth system. Moreover, the time delay can use the same value for a given period of time, regardless of the frequency band, and only the unitary matrix can be configured differently according to each frequency band. In short, the time delay and the GPSD unitary matrix can be configured independently.

The configuration of the time delay and / or unitary matrix - option 2 implementation

If the base station (BS) assigns and notifies the mobile station (MS) of a specific time and / or a specific unitary matrix, the MS can then configure the time delay and / or the unitary matrix as supplied with the BS and transmit accordingly.

If the amount of data (eg, feedback information) received by the BS exceeds the size of the buffer, then the MS may need to, for example, retransmit the data. Given these possibilities, values associated with a specific time delay and / or unitary matrix can be determined.

The configuration of the time delay and / or unitary matrix - option 3 implementation

The BS may refer to the feedback information sent from the MS in determining the time delay and / or the unitary matrix. Moreover, the BS may use a specific time delay and / or unitary matrix to transmit data in the downlink direction. Feedback information may be transmitted periodically, and the BS may reconfigure the time delay and / or the unitary matrix each time feedback information is received.

The configuration of the time delay and / or unitary matrix - option 4 implementation

The GPSD time delay can be configured differently based on the amount of resources allocated to the transmitter (e.g., BS or MS). For example, if the amount of resources allocated to the transmitter is large, the probability of mutual interference of the subcarriers may be small, hence, the time delay can be set to 0 or a relatively smaller value. Alternatively, if the amount of allocated resources is small, a larger time delay value may be set in order to reduce mutual interference between subcarriers.

The configuration of the time delay and / or unitary matrix - option 5 implementation

A specific unitary matrix may be selected as a unitary GPSD matrix by a BS. More specifically, a specific column of a selected unitary matrix may be selected and / or used.

As shown in table 2, the number of columns can be determined according to the compression ratio during data transmission. The BS may determine the specific unitary matrix to be used by GPSD, and may refer to the multiplexing coefficient returned by feedback from the MS in order to determine the number of columns corresponding to the multiplexing coefficient for the selected unitary matrix. In addition, the BS may provide to the MS information about the selected unitary matrix (or unitary matrix index) and information about the selected column (or subindex for the column) of the corresponding unitary matrix.

If the amount of data (eg, feedback information) received by the BS exceeds the size of the buffer, then the MS may need to, for example, retransmit the data. Given these possibilities, a separate column of a particular unitary matrix and / or the corresponding unitary matrix can be selected.

The configuration of the time delay and / or unitary matrix - option 6 implementation

The time delay and the GPSD unitary matrix may be performed according to the manner in which the BS delivers the necessary values to the MS during network entry, and the MS uses the provided values for data transmission. Alternatively, the BS may determine the necessary values and use these values to transmit data in the downlink direction.

The configuration of the time delay and / or unitary matrix - option 7 implementation

The GPSD time delay can be configured differently based on the multiplexing factor. For example, if the multiplex factor is 1, the time delay can be set to 1/2, and if the multiplex factor is 2, the time delay can be set to 1/4. The present embodiment may be used in connection with Embodiment 5, in which a single column is selected from a unitary matrix.

The configuration of the time delay and / or unitary matrix - option 8 implementation

GPSD time delay can be configured differently according to the data distribution scheme. For example, if the MS signal is spaced and distributed over the frequency domain in order to achieve a gain from the frequency diversity, the time delay can be set relatively large in order to optimize the effect of the gain from the frequency diversity. Moreover, if the gain from frequency scheduling is achieved by assigning MS signals close to each other in the frequency domain and assigning MS signals in the frequency domain having a good channel interval, the time delay can be set relatively smaller in order to optimize the gain from scheduling.

The configuration of the time delay and / or unitary matrix - option 9 implementation

The GPSD time delay can be configured differently based on the mobility rate of the MS. For example, if the mobility rate of the MS is slow, the time delay can be set small, since the interference between the subcarriers is relatively small. Alternatively, if the MS mobility rate is fast, the time delay may be large since the interference between the subcarriers is relatively large.

The configuration of the time delay and / or unitary matrix - option 10 implementation

GPSD time delay can be configured differently based on the types of multi-antenna system. For example, if single-user MIMO is used, the time delay can be set as a small value, since the need to take into account mutual interference between subcarriers is relatively small, as is the case with STC. Alternatively, if multi-user MIMO is used (for example, multiple access with a single partition), the time delay can be large, since dedicated subcarriers between / among users need to be sensitive to mutual interference between subcarriers.

The configuration of the time delay and / or unitary matrix - option 11 implementation

GPSD time delay can be configured differently according to user traffic types. For example, if the user traffic is unicast traffic or multicast traffic, the time delay may be set in a variable manner to small or large depending on the condition or condition. However, if the user traffic is broadcast traffic, the time delay may be large since the transmission occurs to a relatively large number of users.

The configuration of the time delay and / or unitary matrix - option 12 implementation

The GPSD time delay can be configured differently based on the number of MSs in the serving cell. For example, if a large number of MSs belong to a cell, the time delay can be set to a large value, and if a small number of MSs are located in a cell, then the time delay can be set to a small value.

The configuration of the time delay and / or unitary matrix - option 13 implementation

The GPSD time delay can be configured differently based on the condition or condition of the cell. For example, a cell can be classified as an isolated cell (e.g., an active point) or a multiple cell, and, in an isolated cell, the time delay can be set to a small value, while a large value for the time delay is set in the multiple cell.

The configuration of the time delay and / or unitary matrix - option 14 implementation

The GPSD time delay can be configured differently according to the size of the granularity transmitted per frequency unit or time unit. For example, if the frequency granularity is fine (i.e., fine granularity), the time delay can be set to a large value, since data loss due to mutual interference must be taken into account. However, if the frequency granularity is coarse (i.e., coarse granularity), then the time delay is set to a small value. In addition, the same logic or scheme as for frequency granularity can be applied to time granularity.

The configuration of the time delay and / or unitary matrix - option 15 implementation

The GPSD time delay can be configured differently based on the size of the codebook. For example, if the system uses a coding table containing a small number of precoding matrices, the time delay can be set to a large value, whereas if the coding table contains a large number of precoding matrices, then the time delay can be set to a small value.

The configuration of the time delay and / or unitary matrix - option 16 implementation

The GPSD time delay can be configured differently based on the number of transmit antennas. For example, a relatively lower time delay value is configured in a system that has a large number of transmit antennas, since the time delay for each antenna must propagate within a fixed period of the prescribed lifetime (TTL). For the same reason, but from the opposite angle, the time delay is set to a large value if the number of transmitting antennas is small.

The configuration of the time delay and / or unitary matrix - option 17 implementation

GPSD time delay can be configured differently based on channel quality information sent from the MS. For example, a receiver may measure channel quality and calculate a modulation and coding scheme (MCS) level indicator according to the measured channel quality. After that, the MCS level indicator can be returned feedback (or transmitted) to the BS. Typically, if the MCS level is high, which indicates acceptable channel quality, the time delay is set to a small value.

Transmitter / receiver for performing phase shift-based precoding

7 is an exemplary diagram illustrating OFDM-based SCW transmitter and receiver using phase shift-based precoding. 8 is an exemplary diagram illustrating an OFDM-based MCW transmitter and receiver using phase shift-based precoding.

Typically, a communication system comprises a transmitter and a receiver. A device that can act as a transmitter and receiver may be referred to as a transceiver. In other words, a transceiver is a combination of a transmitter and a receiver. However, in order to accurately describe the function of the feedback information, the transmitter and receiver can be discussed independently.

In the downlink direction, the transmitter may be part of the BS, and the receiver may be part of the MS. Alternatively, the transmitter may be part of the MS, while the receiver may be part of the BS. A BS may include multiple transmitters and / or receivers. Similarly, the MS may include multiple transmitters and / or receivers.

The functions of the receiver are opposite (or are inverse) to those of the transmitter and are performed in the reverse order. Essentially, the discussions that follow will focus on describing the functions of the transmitter.

7 and 8, the transmitter comprises a channel encoder (510, 610), an interleaver (520, 620), an inverse fast Fourier transform (inverse FFT) unit (550, 650), and an analog converter (560, 660) in addition to the components which are described in FIG. Since the functions are described with respect to FIG. 1, a discussion of these functions will be omitted. Here, a preliminary encoder (540, 640) will be explained in detail.

The precoder (540, 640) further comprises a pre-coding matrix determination module (541, 641) and a pre-coding module (542, 642). More specifically, the precoding matrix determination module (541, 641) can be used to determine the phase shift-based precoding matrix in the form of any one of equations (12), (14), (15), (20) and (21). Details on how to determine the precoding matrix are discussed above, so further discussion will be omitted. Moreover, the precoding matrix determination module (541, 641) can be determined according to embodiments 1-3 of the configuration of the phase shift ratio.

In addition, the precoding module (542, 642) can be used to perform the precoding operation by multiplying OFDM symbols for the respective subcarriers by the phase shift-based precoding matrix, which is determined according to the precoding matrix determining module (541, 641).

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (14)

1. A method of transmitting data using phase shift-based precoding in a multi-antenna system using multiple subcarriers, the method comprising the steps of:
determining a diagonal matrix for providing different phase angles of each of the plurality of antennas as part of a matrix based on a phase shift precoding;
selecting a unitary matrix from the first coding table as part of a phase shift-based precoding matrix; and
perform precoding with respect to the symbols associated with the subcarriers based on the diagonal matrix and the unitary matrix. 2. The method according to claim 1, additionally containing stages in which:
selecting a precoding matrix from the second encoding table;
perform precoding with respect to the symbols associated with the subcarriers based on the selected precoding matrix, the diagonal matrix, and the unitary matrix. 3. The method according to claim 1, in which the unitary matrix is selected after the indices of the respective subcarriers are calculated for the coding table with a given size. 4. The method according to claim 1, in which at least one phase angle of the diagonal matrix and the unitary matrix varies in time. 5. The method according to claim 1, in which the diagonal matrix provides a linear increase in phase angles for adjacent antennas. 6. The method according to claim 1, in which the diagonal matrix allows the phase angles for antennas with even numbers and antennas with odd numbers to alternatively have the same phase angles. 7. The method according to claim 1, in which the diagonal matrix allows a separate antenna having a high correlation with other antennas to have a different phase angle. 8. The method according to claim 1, in which at least one phase angle of the diagonal matrix and the unitary matrix is determined differently, according to the selected frequency band. 9. The method according to claim 1, in which at least one phase angle of the diagonal matrix and the unitary matrix is used when the receiver determines the state of the channel and sends it to the transmitter. 10. The method according to claim 1, in which at least one phase angle of the diagonal matrix and the unitary matrix is used when the transmitter takes into account the feedback information sent from the receiver. 11. The method according to claim 1, in which the time delay corresponding to the phase angle of the diagonal matrix is determined differently according to the multiplexing coefficient. 12. The method according to claim 1, in which the time delay corresponding to the phase angle of the diagonal matrix is determined differently according to the number of transmitting antennas. 13. A device for transmitting data using phase shift-based precoding in a multi-antenna system using multiple subcarriers, the device comprising:
a precoding matrix determination module configured to determine a diagonal matrix for at least one phase shift and a coding table, and a phase shift-based precoding matrix based on a diagonal matrix and a unitary matrix; and
a precoding unit configured to perform precoding on the symbols of the respective subcarriers based on the diagonal matrix and the unitary matrix. 14. The device according to item 13, in which:
the precoding matrix determination module is further configured to select a precoding matrix from the second coding table and to determine a phase shift-based precoding matrix based on a diagonal matrix, a unitary matrix, and a precoding matrix; and
the precoding module is further configured to perform precoding on the symbols of the associated subcarriers based on the precoding matrix, the diagonal matrix, and the unitary matrix.

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